In the realm of note taking and personal knowledge management apps, I've been shopping around recently.
Notion is very popular, and Roam Research [0] has been the popular scrappy upstart that people have been looking at, but I've been unhappy with these since neither has an API (and neither are open source.)
I would _strongly_ urge HN readers to take a look at Tiddlywiki [1]. It's popped up on Hacker News before, and I wrote it off, but I've been taking a closer look recently and its _incredibly_ powerful, as well as completely customizable and open source. It runs off of a micro-kernel architecture, so the core application itself is implemented in code that you can change, edit, and manage just like you would do with your own notes. It's really easy to get started (it's a self contained HTML file) but seems so have some robust saving and backup functionality.
Please please give it a look if you're looking at tools in this space. I've already started using it and I'm _very_ happy with it.
(Not affiliated with Tiddlywiki, just a really happy user.)
Have you found anything like a hybrid between OneNote for its drawing/handwriting-with-stylus support + Roam or TiddlyWiki for the graph-like organization?